Recently, along with rapid progress in network technology and distribution of portable terminals, use of a variety of on-line services is rapidly increasing.
According to the rapid increase in the use of on-line services, service providers of the respective services indiscreetly collect personal information but cannot appropriately manage the collected personal information.
For example, Korean Patent Publication No. 10-2009-0056324 discloses a method for providing personal information of a user to other on-line sites once the user registers the personal information in an on-line site.
According to the conventional authentication methods, users' identities or other identity information susceptible to exposure to a third party due to divergence of personal information was left out of consideration in acquiring personal information of service users and performing authentication using the acquired personal information.
In particular, in the services requiring strict security to prevent identities of the service users, service providers' negligence or misconduct may bring about exposure of users' identities.